Control of the reactions and processes involved in metabolism is essential in order for an organism to maintain the steady-state condition of life. We have recently shown that the reduction of a coordinated nitrosyl ligand (NO) as well as the reactivity of that ligand is controlled by the stereochemistry about the transition metal. Moreover, we have suggested that stereochemical control is a general feature of reactions catalyzed by transition metals. Control of the reactions of the ligands N2 and O2 is directly related to the reduction of nitrogen by nitrogenase, to the binding and transport of oxygen by hemoglobin and myoglobin, and to biological electron transport. The role of stereochemistry in controlling reactions of these ligands will be assessed by preparing appropriate complexes of N2, O2, and NO, by determining the structures of the complexes with x-ray crystallography, by thoroughly characterizing the complexes spectroscopically, and by comparing the chemical reactions of the compounds.